Assume two sites A and B with file server at either end. The contents of /storage should be synchronized between the sites, preserving ownership and permissions. There's no all encompassing group that group-owns all of the files in /storage. If running Unison or rsync pid=0 it is trivial to do the synchronization. However SSH is to be used as transport and for obvious reasons SSH root login has been disabled on both ends.

How can I keep A and B synchronized with all permissions preserved in that situation. Two methods I can think of:

  • Running a secondary SSH that permits root logins yet may only connect over a VPN between A and B.
  • adding a special synchronization user which sshd configuration forcibly executes a
    • SUID wrapper to Unison or rsync (dangerous to get right).
    • sudo wrapper to Unison or rsync

The answers given to the Question Remotely use root over ssh for unison suggest enabling password-less pubkey root login over SSH – I'm not very keen of that solution.

Any other ideas?


The public key root login over SSH is likely your best bet. You could furthermore restrict this access to a single host:

AllowUsers root@

Or even use the Match directive to get a unique configuration for a given something (address, user, etc):

Match Address
    PasswordAuthentication no
    RSAAuthentication yes
    PubkeyAuthentication yes
    PermitRootLogin yes

How to run remote unison instance as root:

Remote side

  • don't touch your sshd config, especially don't create any special synchronization [ssh] user as you state in your question

  • create sudo wrapper vi sunison:

su --preserve-environment -c `which unison` "$@"

(yes, this is for Termux environment, simplify to your needs)

Client side

  • run unison with -servercmd sunison
  • or add to your unison profile servercmd = sunison


  • something like servercmd = sudo unison would be best, but it didn't work for me

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.